Potassium cetyl phosphate is the potassium salt of an organic phosphate ester that is used in a variety of cosmetics and personal care products as a surfactant and emulsifier.
Potassium cetyl phosphate is a potassium salt of a complex mixture of esters of phosphoric acid and cetyl alcohol, a multi-functioning fatty alcohol. It is classified as an alkyl phosphate. The ingredients in the alkyl phosphate family share a common phosphate core structure, and vary by the identity of the alkyl chains (ranging from 8 to 22 carbons in length) attached. Potassium cetyl phosphate has a 16 carbon chain.
In cosmetics and personal care products, potassium cetyl phosphate functions as a surfactant and emulsifier. It can be found in products such as shampoos, facial cleansers, exfoliants, sunscreens, moisturizers, and makeup removers. According to the the FDA’s Voluntary Cosmetic Registration Program (VCRP) data from 2014, potassium cetyl phosphate is reported to be used in 375 formulations, the majority of which are leave-on formulations.
The primary function of potassium cetyl phosphate is as a surfactant. Surfactants are useful cosmetic ingredients because they are compatible with both water and oil. In a solution, surfactants naturally create structures with lipophilic portions aligning with lipids and hydrophilic portions aligning with water. This property makes surfactants ideal for cleansing formulations. For example, while rinsing with water can remove some dirt, oily deposits tend to adhere to the more lipophilic surfaces of hair and skin. After topical application of a surfactant, the lipophilic portion will emulsify these oily deposits while the hydrophilic portion allows them to lift off the surface of skin or hair where the rinse water washes them away.
Surfactants also function as wetting agents by lowering the surface tension between two substances, such as two liquids or a liquid and a solid. This enables surfactants to spread more easily on the surface, as well as prevent a product from balling up on the surface. This property makes potassium cetyl phosphate a useful ingredient in creams and lotions.
Another function of potassium cetyl phosphate is as an emulsifier. An emulsifier is needed for products that contain both water and oil components. Mixing water and oil together creates a dispersion of oil droplets in water (and vice versa). However, these two phases can separate if the product is left to settle. To address this problem, an emulsifier like potassium cetyl phosphate can be added to the system. Emulsifiers improve the consistency of a product, which enables an even distribution of topical skin care benefits.
Potassium cetyl phosphate is primarily used as a co-emulsifier with low HLB non-ionics. HLB (Hydrophile-Lipophile Balance) is an empirical expression for the relationship of the hydrophilic and lipophilic groups of a surfactant. A low HLB (less than 10) means that the substance is soluble in oil, thus, potassium cetyl phosphate is used to create oil-in-water emulsions.
The Cosmetic Ingredient Review (CIR) Expert Panel reviewed the safety of 28 alkyl phosphate ingredients, including potassium cetyl phosphate, as used in cosmetic formulations. The Panel concluded that these ingredients are safe in the present practices of use and concentration in cosmetics when formulated to be non-irritating.
Despite the approval by the CIR Expert Panel, many medical experts believe that cetyl alcohol (a component of potassium cetyl phosphate) can be irritating for those with sensitive skin. Synthetic fatty alcohols like cetyl alcohol are thought to alter the lipid bilayer of the epidermis and cause allergic dermal reactions. With this information, it is best that those with sensitive skin or skin conditions like eczema, rosacea, or psoriasis perform a patch test with any product containing potassium cetyl phosphate.
References: Cosmetic Ingredient Review, “Safety Assessment of Alkyl Phosphates as Used in Cosmetics”, 2014, Truth In Aging, “Potassium Cetyl Phosphate”, American Oil Chemists’ Society, “An introduction to cosmetic technology”, 2015.